A review of reverse Brayton air cycle refrigerators

Currently, the alternative refrigerant in air conditioning systems has become a global problem, and air as a natural working fluid has several advantages of zero ODP, low GWP and satisfactory thermodynamic properties, thus it is a long-term development. However, the poor performance of reverse Brayton air cycle limits their application, and how to improve the performance is the main problem we must face at present. Thus, enhancing the components' efficiency and improving the system comprehensive performance have become the most effective way. The output power produced by the expander can be used for coaxial compressors, such as tur-boexpander compressor (TEC), turbocharger, and rotary vane compressor-expander (ROVCE). What's more, amounts of new technological approaches have been used to improve the performance of the systems such as regeneration, multi-stage compression, mixed working fluid, water removal and integrated system. In addition, thermodynamic optimization methods have become one of the most important approaches to reduce the irre-versible losses and enhance the system performance. At present, reverse Brayton air cycle machines have been applied in various fields such as food freezing, transportation, heat pump, refrigerator, and dryer, etc. With the increasingly stringent environmental laws and regulations, the air cycle system will have a wide perspective application in the future.